I've done this map copying and pasting single elements that I had previously created. Trees have been drawn using a custom brush.

52992

I'm not completely happy with this - I'm still experimenting this approach.
But you can grab the photoshop file with all the elements (mountains, citadels etc) here http://sites.google.com/site/lagrandequestdowload/MapTemplate.psd
And the custom brush is here http://sites.google.com/site/lagrandequestdowload/Albero.abr